Sumanth Banda

Determination of the orientation distribution function in aligned single wall nanotube polymer nanocomposites by polarized Raman spectroscopy

This work focuses on the derivation of the orientation distribution function (ODF) for a uniaxial-axially symmetric system using polarized Raman spectroscopy. A numerical methodology is proposed to determine the ODF that is formulated in terms of Legendre polynomials and the principle of maximum information entropy. The ultimate goal is to quantify the alignment of single wall nanotubes (SWNTs) in a polymer matrix using the experimental information from the Raman intensity. Some of the mathematical and numerical steps in the determination of ODF, not clarified in the current literature, are shown in this work. The proposed numerical methodology to obtain the ODF is illustrated using an experimental case. Electric field–aligned SWNT-urethane dimethacrylate/1,6-hexanediol dimethacrylate nanocomposites are investigated at different processing conditions to bring forward factors that may enhance the alignment of SWNT inclusions in the polymer. ODF results indicate that the higher electric field frequencies produce a good alignment of the SWNT inclusions; a result also corroborated by optical microscopy imaging and electrical conductivity measurements.

A tribological and biomimetic study of PI–CNT composites for cartilage replacement

This article presents an investigation into the possible matching of mechanical properties of a polyimide (PI)–carbon nanotube (CNT) composite system to natural cartilage tissue. Currently used ultrahigh molecular weight polyethylene (UHMWPE) used in total joint replacements presents certain drawbacks due to a mismatch in mechanical and tribological properties with those of a natural bone joint. Natural cartilage tissue is a composite material itself, being composed of collagen fibers, hydrophilic proteoglycan molecules, cells and other constituents. The current investigation attempts to mimic the mechanical and tribological properties of natural cartilage tissue by varying the CNT concentration in a PI matrix. Nanoindentation and pin-on-flat tribological tests were conducted for this purpose. It was found that the coefficient of friction (COF) reached a minimum at a concentration of 0.5% CNT (by volume) when articulated against Ti6Al4V alloy. When articulated against Ti6Al4V alloy in the presence of a lubricant, the minimum COF was obtained at a concentration of 0.2% CNT. The maximum penetration depth under nanoindentation varied with CNT concentration and indicated that the mechanical properties could be tailored to match that of cartilage tissue. A closer investigation into this behavior was carried out using scanning electron, transmission electron, and atomic force microscopy. It was noticed that there is good bonding between the CNTs and polyimide matrix. There was a ductile to brittle transition as the concentration of CNT was increased. Competing interactions between nanotube–matrix and nanotube–nanotube are possible reasons for the deformation and friction behavior identified.

Electric field alignment of single wall carbon nanotubes (SWNT) in polymers

Electrospinning of a SWNT-polyimide composite is accomplished under DC electric field. The resulting composite fibers are characterized to assess the alignment of the SWNTs in the polyimide. Polarized Raman spectroscopy is performed using a Nicolet dispersive Raman spectrometer with a polarizer. The Raman spectrum of SWNT-polyimide fibers is recorded at several angles between the SWNT axis and the incident polarization, in the range of 0° to 180°. The Raman peak in each spectrum corresponds to the tangential mode (1590 cm-1) of the SWNT in the composite. Inspection of the spectra reveals that the maximum intensity is obtained when the polarization of incident radiation is parallel to the SWNT axis, while the smallest intensity is obtained when the polarization of incident radiation is perpendicular to the SWNT axis. Difference in the intensities when the radiation is parallel and perpendicular to the SWNT axis indicates preferential alignment of SWNTs in the polyimide fibers.

Aligned carbon nanotube-polymer composites: investigating their electrical and physical characteristics

Single wall carbon nanotube (SWNT)-polymer composites aligned by an AC electric field were characterized using Raman spectroscopy and electrical conductivity measurements to assess the resulting alignment. The Polarized Raman spectra was recorded at several angles between the SWNT axis and the incident polarization ranging from 0° to 180°. Inspection of the spectra revealed that maximum intensity is obtained when the polarization of incident radiation is parallel to the SWNT axis (0° and 180°), while the smallest intensity is obtained when the polarization of incident radiation is perpendicular to the SWNT axis (90°). The electrical measurements were made in three directions; parallel to the aligned SWNTs and perpendicular to the aligned SWNTs. Based on the electrical conductivity and polarized Raman spectroscopy measurements, it can be concluded that the SWNTs in the polymer matrix were preferentially aligned by applying an AC electric field of 43.5 V/mm at a frequency of 1 Hz, 10 Hz, 10 KHz and 100 KHz.

Electric Field-Assisted Processing of Anisotropic Polymer Nanocomposites

The performance of nanocomposites is affected by dispersion and patterning of the nanoinclusions in the polymer matrix. In this work, electrical and mechanical properties of single wall carbon nanotube polymer composites are tailored using AC electric fields. While the electric field is applied, the polymer is cured to freeze-in the alignment. The specific objectives are: to achieve efficient dispersion of the nanoinclusions in the polymer solutions; to investigate the alignment in liquid polymers in terms of electric field magnitude and frequency; and to quantify the alignment using electrical characterization in the liquid state and mechanical characterization in the solid state.Copyright

A continuum model for carbon nanotube-infused polyimides

Polyimides are presently being investigated for a wide range of aeronautic, aerospace and industrial applications due to the fact that they have good thermal and chemical resistance yet are flexible. Within the realm of aerospace applications, polyimides can be employed for deployment, positioning, and vibration attenuation of large structures including thin-film membrane mirrors and gossamer antennas. The inclusion of single wall carbon nanotubes raises the conductivity levels to permit electric discharge. Additionally, they augment the electromechanical coupling properties of piezoelectric polyimides to provide them with actuator capabilities. We present a temperature-dependent material model based on elasticity theory which characterizes stiffness through the material as a function of varying concentrations of single wall nanotubes (SWNT). We begin by investigating the temperature affects on the polyimide. We then discuss the effects of SWNT volume concentration on the composite storage modulus. The composite model takes into account the alignment, interphase, and geometry of the SWNTs.

Effect of SWCNT on Tribological Behavior of Polymeric Nanocomposite

The nanoscale structure of single-walled carbon nanotubes (SWCNTs) has unique properties. These nanostructured additives can induce unusual characteristic in many polymer matrix. In one of our recent experiments, it was found that when adding SWCNTs into a polyimide (PI) matrix, friction becomes a function of the concentration of the additive. In this research, we analyze the behavior of the SWCNTs-PI nano-composite using an approximation approach. We report that the frictional behavior of the nanocomposite is dominated by the elastic and plastic deformation through randomly dispersed SWCNTs under different loading conditions. At low concentration of SWCNTs, its elasticity dominates the properties of composite while at higher concentration, plastic behavior of tubes plays a major role in describing the properties of composite.© 2008 ASME

Alignment of multi-walled carbon nanotubes in cellulose EAPap by electric fields

Cellulose Electro-Active Paper (EAPap) has potential as a smart material due to its advantages of biodegradability, lightweight, air actuation, large displacement output, low actuation voltage and low power consumption. However, improvement of its small output force and low actuating frequency band still remain as drawbacks. In this study, asymmetrical arrangement of Multi-Walled Carbon Nanotubes (MWNTs) in cellulose matrix was investigated to resolve drawbacks. Corona discharging technique was used by means of DC electrophoresis of MWNTs in cellulose matrix. To make MWNTs mixed cellulose EAPap, cellulose fibers were well dissolved in 8%(w/w) LiCl/DMAc (N,N-dimethyl acetamide) by swelling procedure followed by solvent exchange technique. MWNTs were well dispersed in the cellulose solution by sonication for 2 hours, and the suspension was spin-coated on an ITO (Indium tin oxide) coated glass, and high DC electric field was given to the spincoated suspension for 3 hours at 40°C. The structure of MWNT/Cellulose film was characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was seen that most of MWNTs were moved and biased toward cathode, and film having double layer-like structure was made.

Active Nanocomposite Polymers: Enhancing Sensing and Actuation Performance

The dispersion of nanoparticles, especially those with high aspect ratio, into polymers has been shown through numerous commercial and academic ventures to yield an array of impressive property enhancements for a surprisingly low volume fraction (<5 vol%) of nanoparticle addition, thus maintaining the inherent processibility of the polymer. In this work, we propose a new generation of sensors and actuators based on a piezoelectric polymer (PVDF) with embedded carbon nanotubes. Polyvinylidene fluoride (PVDF)-double walled carbon-nanotubes (DWNT) composite films are prepared with the goal to develop new polymeric materials with enhanced electrical and electromechanical properties. Electrical conductivity and dielectric properties of polyvinylidene fluoride- double-walled carbon nanotubes composites are investigated as a function of frequency (10 Hz–1 MHz), and as a function of weight fraction (0.01–2 wt%). DWNT and PVDF are mixed under mechanical stirring and sonication. The dispersion is assessed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), indicating a good dispersion. Differential Scanning Calorimetery (DSC) is used to study the effect of DWNTs inclusions on the glass transition temperature, Tg , and the crystallinity of the resulting PVDF composite. The percolation threshold is computed by using the bulk conductivity data and it is found that percolation occurs at about 0.19wt%. These investigations promise to increase our understanding of the mechanisms involved, particularly as related to nanoparticle/polymer interaction. This in turn would allow us to tailor the polymer nanocomposites to yield desired performance in terms of actuation voltage, electroactive strain, blocking stress and response time to name a few.Copyright